Photographic compositions and process



United States Patent 3,353,958 PHOTOGRAPHIC COMPOSITIONS AND PROCESS Jerome Albert Moede, Rochester, N.Y., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Filed Jan. 24, 1964, Ser. No. 339,849 18 Claims. (CI. 9687) ABSTRACT OF THE DISCLOSURE A photosensitive drafting film comprising a polyester film with a subbing layer of a vinylidene chloride/methyl acrylate/itaconic acid copolymer having coated thereon a layer of methyl methacrylate polymer with a Tukon film hardness above KHN and containing a matting agent. This product is then coated with a wash-off gelatino-silver halide photographic emulsion which is bound to the hard matte-containing layer by the polymerization product of a vinyl monomer or mixtures of vinyl monomers polymerized in an aqueous gelatin solution.

This invention relates to flexible film coated with a matted layer for drafting purposes. More particularly the invention relates to such drafting films having an extremely hard surface. Still more particularly, the invention is concerned with such a drafting film which may be overcoated, in turn, with an adhesive subbing layer and/or a photographic emulsion layer. The invention also relates to a process for making such films.

It is known in the prior art to prepare drafting materials consisting of cloth and paper on which there are coated layers of transparentizing materials and layers containing abrasive materials. Considerable improvement has been effected by substituting, for the paper or cloth support, a more durable film base, e.g., one composed of vinylcopolymers, polyesters, or polyamides. A particularly useful drafting film is described in assignees Van Stappen Patent US. 2,964,423 wherein a polyester film base support was coated with a drafting layer having a urea-formaldehyde binder. This drafting film had a relatively hard surface such that sharp lines could be drawn thereon with at least a 6H drafting pencil with no indication of abrasion or break-through of the drafting surface. A need still existed, however, for a drafting film having a hard drafting layer which contained no chemicals capable of cross-linking and hardening the gelatin in subsequently applied light-sensitive silver halide emulsion layers such as required in a wash-off film. Also there was need for a hard polymeric binder which had no tendency to discolor or flake upon aging or upon exposure to ultraviolet radiation. Much of the prior art in the manufacture of drafting films describes processes which require that the layers for the drawing surfaces be coated on hydrophobic films from an organic solvent solution. This method of manufacture requires elaborate coating equipment including expensive solvent recovery systems. The prior art also describes processes that are used to prepare matted layers from polymer latices. However, the layers described are soft unless they contain cross-linking agents because the processes required the use of polymers known to be soft. These polymers normally form continuous films at low temperatures.

It is an object of the present invention to produce a dimensionally stable, durable, high-quality drafting film wherein the drafting layer is extremely hard, waterproof,

non-flaking, and free of crazing, or mud cracking. It is further object to prepare such a film by coating the drafting layer from an aqueous dispersion rather than from an organic solvent system. It is a still further object to prepare a drafting film containing no chemicals capable of cross-linking the gelatin in subsequently applied coating layers. Still other objects will be apparent to one skilled in the art.

The above objects are attained in a drafting film comprising a flexible, biaxially-oriented, highly polymeric 1 polyester film substantially composed of the polyesterification product of at least one dicarboxylic acid and at least one dihydric alcohol having on at least one surface, in order, .(1) a thin layer (e.g., 0.5-4 mg./dm. dry weight) of an adherent film-forming essentially hydrophobic organic vinylidene chloride copolymer containing at least 35% by weight of vinylidene chloride, and (2) a thin layer of a continuous hydrophobic film of methyl methacrylate polymer having a Tukon film hardness greater than about 10 KHN comprising uniformly dispersed, finely-divided, discrete particles of a water-insoluble, translucence-producing solid matting agent having an average particle size from about 0.1 to 10.0 microns. The methyl methacrylate polymer layer is further characterized by the absence of any migratory gelatin cross-linking agent (.i.e., gelatin hardeners).

ln a preferred embodiment of the invention, the above drafting film is over-coated with a substratum comprised of a reaction product prepared by polymerizing, in the presence of a gelatin, at least one vinyl monomer selected from the class consisting of vinylidene chloride, methyl acrylate and ethyl acrylate. At least one surfactant, preferably an amphoteric material such as N-coco- ,B-aminopropionate, c'etyl or other long chain betaine, etc. is normally present in the subbing formulation. This insures uniform coverage of the matte surface while the sub is drying. Light-sensitive, gelatino-silver halide emulsion layers may be applied over such a substratum with excellent anchorage. In a particularly preferred embodiment, a gelatino-silver halide emulsion layer containing a tanning developing agent is applied over the above substratum in order to provide a wash-off film in which'the gelatin is unhardened prior to imagewise exposure and development steps.

The invention also includes the process of preparing a drafting film on the above polymeric polyester film support, subcoated with the above thin layer of a vinylidene chloride copolymer, by (l) coating said support with an aqueous dispersion of a methyl methacrylate polymer having a Tukon film hardness greater than 10 KHN comprising heat-removable coalescent material and uniformly dispersed, finely-divided discrete particles of a water-insoluble, translucence-producing, solid matting agent having an average particle size from 0.1 micron to 10 microns, said aqueous dispersion being characterized by the absence of any migratory gelatin cross-linking agent, (2) drying the film at 60-125 C. and (3) curing at -150 C. to remove the coalescent material. Water and coalescent are substantially removed during the drying step to cause aggregation of the polymer particles into a continuous polymer film. The remaining water and coalescent are removed during the curing step to allow the film to reach maxim-um hardness. Since the temperature ranges overlap, it is possible to use the same temperature for both steps so that they appear to blend into a single step. Glycols, glycol-ethers and glycol-ether esters are acceptable coalescents. The glycols, such as propylene glycol, ethylene glycol and diethylene glycol, are preferred over esters, such as n-butoxy acetic acid, ethyl ester and n-butoxy-(2-ethoxy)acetic acid, ethyl ester, because they are less toxic, they yield mechanically stable (e.g., to pumping and ultrasonic deaeration) and pH stable dispersions and they act as anti-crazing or antimud-cracking agents.

In an exemplary procedure, a dimensionally stable vinylidene chloride/methyl acrylate/itaconic acid copolymer coated polyethylene terephthalate film base as described in Example IV of Alles US. Patent 2,779,684 is coated to a dry thickness of about 0.4 mil with a continuous stratum comprised of a methyl methacrylate polymer having a Tukon film hardness greater than 10 KHN and about 0.2 to 1.0 part by weight per one part of polymer of matte (e.g., silicon dioxide of 1-10 micron particle size), to 0.05 part by weight of a thickener per 1 part of polymer and less than 0.01 part by weight dispersants per 1 part of polymer. Optionally, other surfactants can be added to act as wetting agents. In cases where it is advised to use such a system as a backing layer with reduced matte in conjunction with a drafting layer on the other side, the polymer may approach 100% of the layer. The methyl methacrylate polymer is used in the form of a latex (aqueous dispersion) and the aqueous coating dispersion contains, in addition to the above ingredients, a certain amount of additional water and a coalescent, e.g., ethylene glycol, n-butoxy-(Z-ethoxy) acetic acid, ethyl ester, equal to more than about 40% by weight of the methyl/ methacrylate polymer. It is also advantageous to add a hydrosol of silicon dioxide with the SiO equal to 3 to about- 25% by weight of the methyl methacrylate polymer to improve anchorage of subsequently overcoated layers to the matte layer. The SiO of the hydrosol is of much smaller particle size than that of the matte. The coating dispersion is advantageously treated mechanically, e.g., passed through a sand mill to disperse the pigments before or after adding the polymer latex, depending on the nature of the latex. After coating, the Water and the coalescent are partially removed by drying at a temperature above 60 C. to coalesce the polymer particles into a continuous water-resistant film and curing at 110 to 150 C. to remove the residual water and coalescent and thereby obtain maximum layer hardness. The drying temperature required is inversely dependent on the amount of coalescent added to the coating medium. The uniformity (lack of crazing or mud-cracking) of rapidly dried layers is assured by either using ethylene, propylene, or diethylene glycol as the coalescents or by adding a copolymer of methyl vinyl ether and maleic anhy-dride to the system. Use of these glycols as coalescents also preserves the mechanical stability of the system. The drying and coalescing steps may be carried out very quickly; for example, adequate drying may be achieved in only 20 seconds, and adequate curing in one minute. (Of course longer drying and curing times, e.g., 5 minutes or more, may be used without adversely affecting the properties of the cured layer.) From a practical standpoint, rapid drying and curing are quite advantageous since they make it possible for the layer to be applied at the time the vinylidene chloride copolymer subbed polyester film support is manufactured. Since the temperature ranges of drying and coalescing overlap, the two steps have, upon occasion, been combined into a single operation. Thus both operations could be carried out rapidly in a single step of heating, for example, at 110 to 125 C. for about 1 to 5 minutes. If rapid drying is unnecessary, the steps can be combined to give longer exposure to heat at a lesser heat intensity (e.g., 60 C. for 1 hour).

The element, prepared according to the above exemplary procedure, may be used as a drafting film or may have additional coatings applied so as to become a lightsensitive photographic element. When light-sensitive emulsions are coated on the films, it is essential to use a subbing layer prepared by polymerizing a vinyl monomer, e.g., vinylidene chloride and/ or methyl or ethyl acrylate, in an aqueous gelatin solution, wherein there is a ratio of from 1 to 9 parts of gelatin to 1 part of total monomer on a dry weight basis or to use these polymers as a binder for the emulsion which is directly coated on the film. After the polymerization reaction, the reaction product is diluted considerably with water, and one or more surfactants is added, e.g., sodium N-coco-B-aminopropionate without which the subbing layer pulls away from the edges of the film or flows into rivulets before drying. It may also be desirable to add a hydrosol of silicon dioxide to the subbing composition to improve anchorage of the subsequently applied emulsion layer. Over the subbing layer there may then be applied a conventional gelatino-silver halide photographic emulsion layer, a particularly useful emulsion being one of the wash-off variety, e.g., a gelatinosilver halide emulsion containing a tanning developing agent such as catechol, pyrogallol or hydroquinone, a hardener restrainer such as hydroxylamine, an antihalation dye, and various other additives such as stabilizers and conventional wetting agents. Excellent adhesion of the emulsion to the drafting layer may also be achieved with or without the use of a substratum by using the vinyl polymer-gelatin component as the emulsion binder. Because of the unique composition of the drafting layer, there are no migratory chemicals capable of migrating into the wash-01f emulsion layer and causing cross-linking or hardening of the gelatin therein. Image-wise exposure of the emulsion layer causes hardening of the exposed areas during development with the tanning developer contained in the emulsion. A subsequent washing in warm water removes the wash-off emulsion in the unexposed areas, revealing the original drafting layer surface which is capable of accepting drafting inks and drafting pencil. Corrections and additions can also be made in the exposed area by wet erasure. Furthermore, there is no discoloration or flaking upon prolonged exposure to ultraviolet radiation.

The subbing layer described above provides excellent anchorage to conventional gelatino-silver halide emulsions and the invention is by no means restricted to the use of the particularly-discussed wash-off type of emulsion. Certain combinations of normal gelatin with the gelatin reaction product may also provide the desired adhesion. Also, other surfactants may be used in place of those mentioned above. Although ordinarily not required, the adhesion provided by these formulations may be even improved further by heat treating the subbed acrylic layer at -150 C.

This treatment may be accomplished advantageously by applying the sub to the drafting layer at the time between the drying and curing steps of the drafted layer.

Other useful embodiments of this invention include doubly-coated drafting films. It would be preferred to use the same type of vinylidene chloride copolymer subbing layer on both sides of the polyester film support but the drafting layers themselves need not be identical. Thus, it is sometimes advantageous to provide one side of the drafting film with a very hard surface as described above while the opposite side may be considerably softer. The choice of matting agent is optional in preparing the drafting layer. For example, silicon dioxide is one of the most widely used matting agents in drafting films and gives excellent results when it is desired to draw on the film with a mechanical pencil. On the other hand, silicon dioxide is sufiiciently abrasive that it may cause damage to inking pens. For this reason, it is sometimes desirable to use a softer matting agent such as starch particles, or to use a doubly-coated drafting film wherein one surface contains a hard matting agent and the other surface contains either no matting agent or a relatively soft matting agent. In still another embodiment of this invention, the film may have a drafting layer on both sides of the support and either or both sides of the drafting surface will be overcoated EXAMPLE I A matted acrylic polymer composition comprising the following ingredients was prepared:

Material: Parts by weight Distilled water 18 Silica hydrosol 30% by weight SiO an aqueous colloidal sol of alumina modified silica particles approximately 15 millimicrons diameter in size 15 Ethylene glycol 109 Titanium dioxide pigment (0.1 to microns particle size) 4.2 Silicon dioxide pigment (l to microns particle size) 55.8 Thickener, a copolymer of ethyl acrylate,

methyl acrylate and 20 to 30% methacrylic acid (solids) .65 Dispersant (optional), an ammonium salt of a carboxylated polyelectrolyte (Resinous Products & Chem. Co., Amberlac 165) .1 Isooctyl phenoxy polyethoxy ethanol (surfactant containing 910 ethoxy groups) 2 Polymethyl methacrylate (38 +05% by weight solids), having a Tukon film hardness 20 KHN 263 The composition was prepared for coating by first mixing the water, silica hydrosol, ethylene glycol, pigments, thickener and dispersant. The mixture was then passed through a sand mill to disperse the pigments and then admixed with the surfactant and the polymer latex. A small amount of NH OH was added to adjust the pH to 8.59.5 to stabilize the system.

The matte-polymer mixture was coated on a dimensionally stable vinylidene chloride/methyl acrylate/itaconic acid copolymer coated polyethylene terephthalate film base as described in Example IV of Alles US. Patent 2,779,684, dried for 24 seconds at 1l0120 C., and cured for 3.5 minutes at 130-135" C. to remove the residual ethylene glycol coalescent. The coating mixture was stable to mechanical stresses encountered in pumping, milling, and ultrasonic deaeration. A continuous matted polymer film free of crazing (also called alligatoring or mud-cracking) was obtained. The dry thickness of the layer was between .3 and .6 mil. The product was useful as a drafting film. It accepted drafting inks, and drafting pencil up to 9H without cutting, withstood wet erasure and did not discolor or flake upon prolonged exposure to ultraviolet light.

Part of the matted polymer layer was then coated with a subbing composition comprised of the materials listed below and dried. The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period.

The subbed layer was then coated with a gelatinosilver chloride emulsion containing catechol as a tanning developing agent, hydroxyl amine hydrochloride as a gelatin hardening restrainer, to prevent hardening of the gelatin by exterior agents, an antihalation dye, stabilizer, wetting agents and various other additives as conventionally used in photographic emulsions. The element was given an imagewise exposure to a carbon arc lamp and then developed for 1 minute at 68 F. in an aqueous solu- 6 tion comprising 5% by'weight sodium carbonate. The emulsion was tanned (hardened) in the image area; the non-image emulsion remained unhardened and was washed off in warm water leaving behind a relief image on the matted support. Such a process is useful in making reproductions of drawings, maps, etc., wherein the reproduction can be easily revised by drawing on the matte surface and/ or Wet erasing the relief image. Excellent adhesion was obtained between all layers before and after exposure and photographic processing of the element. Neither the matted acrylic polymer layer nor the substratum contributed to the hardness of the emulsion layer.

Subcomposition 1 The gelatin-polymer component was prepared by copolymerizing 8 parts of vlnylidene chloride and 8 parts of methyl acrylate in the presence of 84 parts of gelatin. The polymerization was carried out in aqueous medium in the presence of a redox catalyst system, e.g., a mixture of ammonium persulfate and sodium metabisulfite, and an anionic surfactant, e.g., sodium lauryl sulfate.

2 Coco represents a mixture of the high molecular weight hydrocarbon radicals corresponding to those present in the esters in coconut oil including, in order of decreasing conciantlratiou, lauryl, myristyl, palmityl, caprylyl, capryl and o ey EXAMPLE II Part of the matted polymer layer prepared in Example I was coated with a subbing composition comprised of the materials listed below and dried. The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period- The subbed layer was then coated with a litho-type gelatino-silver bromochloride emulsion comprising 30 mole percent silver bromide and 70 mole percent silver chloride, an orthochromatic optical sensitizing dye, formaldehyde hardener, gelatin and a polyethylacrylate resin latex equal to 33% of the gelatin on a dry weight basis. Excellent adhesion was obtained between all layers before and after developing and fixing of the exposed and unexposed emulsion.

Subcomposition Material: Parts by weight Water 14150 Gelatin-polymer component (dry wt.) Sodium salt of N-coco-fl-aminopropionate 3.6

Isooctyl phenoxy polyethoxy ethanol (containing 9-10 ethoxy groups) l5 Silica hydrosol (30% SiO as described in Example I 25 1 The gelatimpolymer component was prepared by copolymerizmg 13 parts of vinylidene chloride and 7 parts of methyl acrylate 1n the presence of 75 parts of gelatin. Polymerization was carried out under conditions similar to those described for preparing the gelatinpolymer component of Example I except that the catalyst was hydrogen peroxide.

EXAMPLE III 7 Subcomposition Material: Parts by weight Water 14150 Gelatin-polymer component 1 (dry Wt.) 100 Sodium salt of N-coco-fl-aminopropionate 3.6 Isooctyl phenoxy polyethoxy ethanol (containing about 30 ethoxy groups) Silica hydrosol (30% SiO as described in Example I The gelatin-polymer component was prepared by polymerizing 35 parts of ethyl acrylate in the presence of 60 parts of gelatin. Polymerization was carried out similarly to that described in Example I except that bis-azoisobutyronitrile was used as the catalyst.

EXAMPLE IV A matted acrylic composition comprising the following ingredients was prepared: Material: Parts by weight Silica hydrosol Si having silica particles approximately 15 millimicrons diameter 1 Specific viscosity is determined on a solution of 1 gram of the copolymer in 100 mls. of methylethyl ketone at 29 C.

The composition was prepared for coating by first mixing the silica hydrosol, ethylene glycol and pigments, then passing the mixture through a sand mill to disperse the pigments. The dispersion was then admixed with an emulsified mixture of the coalescents, emulsifier and the latex. The thickener and a small amount of NaOH was added to stabilize the system.

The matte-acrylic polymer mixture was coated on both sides of the polyester film support of Example I, dried for 30 seconds at 93 C. and cured for 2 minutes at 135 C. to remove the coalescents.

A continuous matted polymer film free of cr-azing and having a dry thickness between 0.4 and 0.5 mils was obtained. The product was useful as a drafting film. It accepted drafting inks and at least 6H pencil without cutting, withstood wet erasure and the matte layer did not discolor or flake after prolonged exposure to ultraviolet light.

EXAMPLE V A matted acrylic composition comprised of the following ingredients was prepared: Material: Parts by weight Silica hydrosol (30% SiO having a particle size approximately 7 millimicrons diameter in size 42 Ethylene glycol 17 Copolymer (1:1) of methylvinylether and maleic anhydride, specific viscosity range of 1.52.0, anticrazing agent and thickener 1.8 n-Butoxy acetic acid, ethyl ester, coalescent 10 The composition was prepared for coating by first mixing the water, silica hydrosol, pigments, thickener and n-butoxy acetic acid, ethyl ester and then passing the mixture through a sand mill to disperse the pigments. The dispersion was then admixed with an emulsified mixture of the emulsifier, n-butoxy-(Z-ethoxy)acetic acid, ethyl ester and the latex. A small amount of NH OH was added to stabilize the system.

The matte-acrylic polymer mixture was coated on a polyester film support similar to that of Example I, dried at C. and cured for 3.5 minutes at C. to remove the coalescent.

A continuous matted polymer film free of crazing and having a dry thickness between .30 and .46 mil was obtained. The product was useful as a drafting film. It accepted drafting inks and 6H pencil without cutting, withstood wet erasure and the matte layer did not discolor or flake after prolonged exposure to ultraviolet light.

EXAMPLE VI Example V was repeated except that between the drying and curing steps a sub was applied to the matted polymer layers and dried at 68 C. The sub was composed of:

Water 14160 Gelatin-polymer components 1 (dry wt.) 100 Sodium salt of N-coco-fi-aminopropionate 2 Isooctyl phenoxy polyethoxy ethanol (containing about 40 ethoxy groups) 15 Silica hydrosol (30% SiO as in Example IV 26 The gelatimpolymer component was prepared by copolymerizing 18 parts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. Polymerization was carried out similarly to that described in Example I except that amornnium persulfate alone was used as the catalyst.

The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period.

The subbed layer was then coated with a gelatinosilver halide emulsion. Excellent adhesion was obtained between all layers before and after developing and fixing of the exposed and unexposed emulsion. Neither the mated acrylic polymer layer nor the substratum contributed to the hardness of the emulsion layer.

EXAMPLE VII The composition was prepared for coating by first mixing the water and pigments and thickener, then passing the mixture through a sand mill to disperse the pigments. The dispersion was then admixed with an emulsified mixture of water, the emulsifier and the coalescent and finally the latex. A small amount of NH OH was added to adjust the pH to 8.59.5 to stabilize the system.

The matte-acrylic polymer mixture was coated on a polyester film support the same as in Example I, dried for 30 seconds at 79 C. and cured for 2 minutes at 134 C. to remove the coalescent.

A continuous matted polymer film having a dry thickness between .30 and .36 mil was obtained. The prodnot was useful as a drafting film. It accepted drafting inks and 6H pencil without cutting, withstood wet erasure and the matte layer did not discolor or flake after prolonged exposure to ultraviolet light.

Part of the matted polymer was then coated with a subbing composition comprised of the materials listed below and dried. The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period.

The subbed layer was then coated with a gelatinosilver halide emulsion. Good adhesion was obtained between all layers before and after developing and fixing of the exposed and unexposed emulsion. Neither the matted acrylic polymer layer nor the substratum contributed to the hardness of the emulsion layer.

Subcomposition Material: Parts by weight Water 14000 Gelatin-polymer component 1 (dry wt.) 100 Sodium salt of N-coco-fl-aminopropionate 20 Silica hydrosol (30% SiO as in Example I 100 1 The gelatin-polymer component was prepared by copolymerizing 18 parts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. The polymerization process was similar to that described in Example I.

EXAMPLE VIII A matted acrylic composition comprising the following ingredients was prepared:

Isooctyl phenoxy polyethoxy ethanol, emulsifier, as in Example I 1 n-Butoxy-(2-ethoxy) acetic acid, ethyl ester 40 Methyl methacrylate polymer latex (38% polymer) as in Example I 263 The composition was prepared for coating by first mixing the water, silica hydrosol, pigments, thickener and n-butoxy acetic acid, ethyl ester and then passing the mixture through a sand mill to disperse the pigments. The dispersion was then admixed with an emulsified mixture of the emulsifier, n-butoxy-(Z-ethoxy)acetic acid, ethyl ester and the latex. A small amount of NaOH was added to stabilize the system.

The matte-acrylic molymer mixture was coated on a polyester film support, the same as that of Example I, dried for 30 seconds at 93 C. and cured for 2 minutes at 130 C. to remove the coalescent.

A continuous matted polymer film having a dry thickness between .35 and .60 mil was obtained. The product was useful as a drafting film. It accepted drafting inks and 6H pencil without cutting, withstood wet erasure and the matte layer did not discolor or flake after prolonged exposure to ultraviolet light.

Part of the matted polymer layer was then coated with a subbing composition comprised of the materials listed below and dried. The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period.

10 The subbed layer was then coated with a gelatinosilver halide emulsion. Excellent adhesion was obtained between all layers before and ater developing and fixing of the exposed and unexposed emulsion. Neither the matted acrylic polymer layer nor the substratum contributed to the harness of the emulsion layer.

Subco mposition Material: Parts by weight Water 14150 Gelatin-polymer component (dry wt.) Sodium salt of N-coco-B-aminopropionate 3.3

Isooctyl phenoxy polyethoxy ethanol as in Example I 15 Silica hydrosol (30% SiO as in Example I 25 1 The gelatin-polymer component was prepared by copolymerizing 18 par-ts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. The polymerization process was similar to that described in Example I.

EXAMPLE IX A matted acrylic polymer composition comprising the following ingredients was prepared:

Material: Parts by weight Methyl methacrylate polymer latex 38% polymer) as in Example I 263 Silica hydrosol (30% SiO as in Example IV l5 Silicon dioxide pigment as in Example I 55.8 Titanium dioxide pigment as in Example I 4.2 Thickener as in Example I (solids) 0.65

Propylene glycol, coalescent 75 The composition was prepared for coating by first mixing the latex, silica hydrosol, pigments and thickener. A small amount of NaOH was added to adjust the pH to 9.1 to stabilize the system. The mixture was then passed through a sand mill to disperse the pigments. The propylene glycol coalescent was then added and the resulting mixture was coated on a polyester film support similar to that of Example I, dried for 30 seconds at C. and cured for 2 minutes at C. to remove the coalescent. The coating mixture was stable to mechanical stresses encountered in pumping and milling. A continuous matted polymer film free of crazing was obtained. The dry thickness of the layer was between .3 and .5 mil. It accepted drafting ink and drafting pencil up to 9H without cutting, withstood wet erasure and did not discolor or flake after exposure to ultraviolet light.

Part of the matted polymer layer was then coated with a subbing composition comprised of the materials listed below and dried. The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period.

The subbed layer was then coated with a gelatino-silver halide emulsion. Excellent adhesion was obtained between all layers before and after developing and fixing of the exposed and unexposed emulsion. Neither the matted acrylic polymer layer nor the substratum contributed to the hardness of the emulsion layer.

Subcomposition Material: Parts by weight Water 14150 Gelatin-polymer component (dry wt.) 100 Sodium salt of N-cocmfi-aminopropionate 6.8

Isooctyl phenoxy polyethoxy ethanol as in Example I 15 Silica hydrosol (30% SiO as in Example I 25 1 The gelatin-polymer component was prepared by Copolymerizing 18 parts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. The polymerization process was similar to that described in Example I.

1 1 EXAMPLE X A matted acrylic polymer composition comprised of the following ingredients was prepared:

Material: Parts by weight Water 90 Rice starch 46 Silicon dioxide pigment 14 Methyl methacrylate polymer latex (38% polymer) as in Example I 263 Propylene glycol, coalescent 100 Thickener as in Example I (solids) .65

The composition was prepared for coating by first mixing the water, starch and pigment and then ball milling to effect dispersion. The dispersion was then admixed with the latex coalescent and thickener. A small amount of NaOH was added to stabilize the system.

The matte-polymer mixture was coated on a polyester film support, the same as Example I, dried for 30 seconds at 110 C. and cured for 2 minutes at 135 C. to remove the coalescent. The coating mixture was stable to mechanical stresses encountered in pumping and milling. A continuous matted polymer film free of crazin-g was obtained. The dry thickness of the layer was between .2 and .4 mil. The product was useful as a drafting film. It caused less wear on drafting pens than layers containing a higher percentage of SiO pigment. It accepted drafting ink and drafting pencils up to 9H without cutting, withstood wet erasure, and did not flake upon exposure to ultraviolet light.

Part of the matted polymer layer was then coated with a subbing composition comprised of the materials listed below and dried. The composition coated uniformly and remained uniformly spread over the surface of the matte layer throughout the drying period.

The subbed layer was then coated with a gelatino-silyer halide emulsion. Good adhesion was obtained between all layers before and after developing and fixing f the exposed and unexposed emulsion. Neither the matted acrylic polymer layer nor the substratum contributed to the hardness of the emulsion layer.

Subcomposition Material: Parts by weight Water 14150 Gelatin-polymer component 1 (dry wt.) 10 0 Sodium salt of N-coco-B-aminopropionate 6. 8 Isooctyl phenoxy polyethoxy ethanol as in Example I I. Silica hydrosol (30% SiO as in Example I 1 The gelatin-polymer component was prepared by copolyrnerizing 18 parts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. The polymerization process was similar to that described in Example L.

EXAMPLE XI A matted acrylic polymer composition comprising the following ingredients was prepared:

The composition was prepared for coating by first mixing the water, starch and. pigment and then ball milling to effect dispersion. The dispersion was then admixed with the latex coalescent, and thickener. A small amount of NaOI-I was added to stabilize the system.

The matte-polymer mixture was then coated on a polyester film support the same as Example I, dried for 12 seconds at C. and cured for 2 minutes at 135 C. to remove the coalescent. The coating mixture was stable to mechanical stresses encountered in pumping, milling, etc. A continuous matted polymer film free of crazing was obtained. The dry thickness of the layer was between .3 and .5 mil. The product was useful as a drafting film. It caused less wear on drafting pens than layers containing a higher percentage of SiO pigment. It accepted drafting ink and drafting pencils up to 9H without cutting, withstood wet erasure and did not flake upon exposure to ultraviolet light.

EXAMPLE XII A matted acrylic polymer composition comprising the following ingredients was prepared:

Material: Parts by weight Distilled water 24 Silica hydrosol (30% SiO 20 Ethylene glycol 145 Titanium dioxide pigment as in Example I 5.6

The composition was prepared for coating by first mixing the water, silica hydrosol, ethylene glycol, pigments, thickener and dispersant. The mixture was then passed through a sand mill to disperse the pigments and then admixed With the polymer latex. A small amount of NH OH was added to adjust the pH to 8.59.5 to stabilize the system.

The matte-polymer mixture was coated on a polyester film support the same as in Example 1, dried for 30 seconds at 110-120 C. and cured for 2 minutes at C. to remove the ethylene glycol coalescent. The coating mixture was stable to mechanical stresses encountered in pumping. A continuous matted polymer film free of crazing (also called alligatoring or mud cracking) was obtained. The dry thickness of the layer ranged from .2 to .6 mil. The product was useful as a drafting film. It accepted drafting inks, and drafting pencil up to 9H Without cutting, withstood wet erasure and did not discolor or flake upon prolonged exposure to ultraviolet light.

EXAMPLE XIII The matted acrylic composition comprising the following ingredients was prepared:

Material: Parts by weight Water 20 Silicon dioxide pigment as in Ex. I 27.3 Titanium dioxide pigment as in Ex. I 2.7 Thickener as in Ex. VII .35 An isooctyl phenyl polyethoxy ethanol, emulsifier 2 n-Butoxy-(Z-ethoxy) acetic acid, ethylester,

coalescent 70 Methyl methacrylate polymer latex (38% polymer) (Tukon film hardness of 20 KHN) 263 The composition was prepared for coating by first mixing the water and pigments and thickener, then passing the mixture through a sand mill to disperse the pigments. The dispersion was then admixed with an emulsified mixture of water, the emulsifier and the coalescent and finally adding the latex. A small amount of NaOH was added to adjust the pH to 8.59.5 to stabilize the system.

The matte-acrylic polymer mixture was coated on a polyester film support the same as Example I, dried for 30 seconds at 80 C. and cured for 2 minutes at 125 C. to remove the coalescent.

A continuous matted polymer film having a dry thickness ranging from .2 to .36 mil was obtained. The product 13 was useful as a drafting film. It accepted drafting inks and 6H pencil without cutting, withstood wet erasure and the matte layer did not discolor orflake after prolonged exposure to ultraviolet light.

Part of the mated acrylic layer was then coated with a wash-off type emulsion of the same composition as that used in Example I except that the gelatin binder was replaced by a gelatin-polymer component prepared by copolymerizing, 12 parts of vinylidene chloride and 4 parts of methyl acrylate in the presence of 84 parts of gelatin. The polymerization was carried out in an aqueous system in the presenceof a redox catalyst system, e.g., a mixture of ammonium persulfate and sodium metabisulfite, an ionic surfactant, e.g., sodium lauryl sulfate. Excellent adhesionwas obtained between all layers before and after photographic processing of the exposed and unexposed emulsions. Neither thejmatted polymer layer nor the emulsion itself contained any material that contributed to the hardness of the emulsion layer prior to exposure and tanning development. A good wash-off relief image was obtained-according to the process of Example I.

EXAMPLE XIV Part of the matted acrylic polymer layer prepared in Example XIII was coated with an emulsion of the same composition as that used in Example I except that the gelatin binder was replaced by a gelatin-polymer component prepared by copolymerizi-ng 18 parts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. Polymerization was carried out under conditions similar to those described for preparing the gelatin-polymer component of Example I, except that the catalyst was hydrogen peroxide. Excellent adhesion was obtained between all layers before and after photographic processing of the exposed and unexposed emulsion. Neither the matted polymer layer or the emulsion itself contained any material that contributed to the hardness of the emulsion layer prior to exposure and tanning development. A good wash-off relief image was obtained according to the process of Example I.

EXAMPLE XV -Part of the matted acrylic polymer layer prepared in Example XIII was coated with an emulsion of the same composition as that used in Example I except that the gelatinbinder was replaced by a gelatin-polymer component prepared by copolymerizing 8 parts of vinylidene chloride and 8 parts of methyl acrylate in the presence of 84 parts of gelatin. The polymerization was carried out in aqueous medium in the presence of a redox catalyst system, e.g., a mixtureof ammonium persulfate and sodium me'tabisulfite, and an anionic surfactant e.g., sodium lauryl sulfate. Excellent adhesion was obtained between all layers before and after photographic processing of the exposed and unexposed emulsion. Neither the matted polymer layernor the emulsion itself contained'any material that contributed tothe hardness of the emulsion layer priorto exposureand tanning development. A good washoffrelief-image was obtained according to the process of Example I.

" EXAMPLE XVI Part of the matted acrylic polymer layer prepared in Example XIII was coated with an emulsion of the same composition as that used in Example I except that the gelatin binderwasreplaced by a gelatin-polymer composure and tanning development. A good wash-off relief image was obtained according to the process of Example I.

EXAMPLE XVII Part of the matted acrylic polymer layer prepared in Example XIII was coated with a subbing composition comprised of the materials listed below and dried at approximately C. The subbed layer was then coated with a wash-off type emulsion like that used in Example I. Good adhesion was obtained between all layers before and after photographic processing of the exposed and unexposed emulsion. Neither the polymer layer nor the substratum contributed to the hardness of the emulsion layer.

Subcomposition Material: Parts by weight Water 14140 Gelatin-polymer component 1 100 Silica hydrosol (30% SiO 28 Isooctyl phenoxy polyethoxy ethanol (containing 9-l0 ethoxy groups) 16 Dispersant, (optional) ammonium salt of a carboxylated polyelectrolyte (Amberlac The gelatin polymer component was prepared by copolymerizing 18 parts of vinylidene chloride and 7 parts of methyl acrylate in the presence of 75 parts of gelatin. Polymerization was carried out under conditions similar to those described for preparing the gelatin-polymer component of Example I except that the catalyst was hydrogen peroxide.

EXAMPLE XVIII A matted acrylic polymer composition comprising the following ingredients was prepared:

Material: Parts by weight Water 60 Silica hydrosol (30% SiO as in Example IV 1O Silicon dioxide pigment as in Ex. V 38.6 Titanium dioxide pigment as in Ex. I 3.9 Dispersant-same as Ex. I 0.1 Propylene glycol 77 'Copolymer of methylvinylether and maleic anhydride having a specific viscosity of 0.14,

thickener and anticrazing agent 5 Methyl methacrylate polymer latex as in Example I 263 The composition was prepared by first mixing the water, silica hydrosol, pigments, dispersant and propylene glycol. The mixture was then passed through a sand mill to disperse the pigments and then admixed with the copolymer and the latex. A small amount of NH OH was added to adjust the pH to 8.5-9.5 to stabilize the system.

The matte polymer mixture was coated on the polyester film support of Example I, dried and cured for 5 minutes at C. to remove the water and coalescent, propylene glycol.

A continuous matted polymer film free of crazing was obtained. The product was useful as a drafting film. It accepted ink and 7H drafting pencil without cutting, withstood wet erasure and did not discolor or flake after exposure to ultraviolet light.

The Tukon hardness of the films .can be adjusted by mixing a specific methyl methacrylate with another acrylic polymer of a different hardness.

Hardness of polymer films is best determined by means of a Tukon Microhardness Tester as described in the Resin Review, vol. -6, pp. 12-14, December 1962, published by Rohm and Haas Company. A load of 25 grams is used in making the reported hardness measurements since, as described in the above reference the Knoop Hardness Numbers, KHN, vary with the load.

To determine the stability to ultraviolet radiation, samples of a matted acrylic layer were exposed to a G.E., 100 watt, S4, mercury vapor sun lamp for 24 hours at a distance of 3 /2 inches. This lamp emits 500600 micro watts per square centimeter between 2600-3700 Angstroms. While it is not essential to have, as separate ingredients, matting agents, pigments and toothing agents, it is necessary for the matting agent to be present. Preferably, the matting agents are present in amounts of about 0.3 to 0.8 part by weight of matte per 1 part of methyl methacrylate polymer. Titanium dioxide, as Well as a number of other materials, can act in more than one capacity, e.g., as a matting agent and/ or opacifying pigment and/ or coloring agent. Other materials which may be used in one or more of these capacities are, for example, silica, ground glass, chalk, talc, diatomaceous earth, magnesium carbonate, starch, barytes, clay, Monastral Fast Blue (C.I. Pigment Blue) and other pigments and dyes. The average particle size of these materials can vary from about 0.1 to 10 microns but preferably have an average particle size of 1 to 10 microns.

In the preferred aspect of the invention the copolymer coated polyester film used to make the drafting film has a thickness from 3 to 10 mils and is dimensionally stable,

that is, it exhibits a shrinkage of not more than 0.2% both in longitudinal and lateral direction when heated free from tension to a temperature of 120 C. for a period of 5 minutes. Suitable copolymer-coated polyester films of the foregoing type are described in Alles U.S. Patent 2,779,684 and in the patents referred to therein. The preferred films, however, have a polyethylene terephthalate base and a vinylidene chloride copolymer layer wherein the addition copolymer contains at least 35 by Weight of vinylidene chloride.

Various conventional coating devices can be used to apply the acrylic polymer latex containing the dispersed particles of toothing agent. Thus, the dispersions can be supplied from a gravity-fed or pressure-fed hopper or they can be applied by dip-coating techniques or by means of bead coating or applicator rolls. The thickness of the coating can be controlled by means of doctor blades or by means of air streams, e.g., air-doctor knives.

In the preferred aspect of the invention, the oriented polyester film base has a vinylidene chloride/ acrylic ester/ itaconic acid copolymer layer container such components in amounts by weight of 35 to 96.0%, 3.5 to 64.5% and 0.5 to 2.5% on one or both surfaces of the oriented polyester base and the drafting layer is coated over the copolymer. The copolymer layer is exceedingly thin, about 0.5-4 mg./dm. and is usually applied to the polyester base prior to orienting it and rendering it dimensionally stable. This vinylidene chloride copolymer coated base, preferably a polyethylene terephthalate film, can be made after the manner described in Alles et a1. U.S. Patent 2,627,088 and Alles US. Patent 2,779,684 and will exhibit shrinking of not more than 0.2% in both longitudinal and lateral directions when not under tension and heated to a temperature of 120 C. for a period of 5 minutes.

The various vinyl esters (including acrylonitrile) which can be used in making the vinylidene chloride copolymers, are those disclosed in the Alles et al. patent. A suitable copolymer may be composed of 75-90% vinylidene chloride, 4 to methyl acrylate and 1 to 5% itaconic acid.

The support need not necessarily be 4-mi1 polyethylene terephthalate film but may be composed of other di mensionally stable polyester films such as are disclosed in Carothers U.S. Patent 2,071,250, andbearing a thin layer of an adherent film-forming essentially hydrophobic copolymer as disclosed in Alles et al. U.S. 2,627,088 and Alles U.S. 2,779,684 and the patents referred to in the specifications of these patents. Other suitable supports are the polyethylene terephthalate/isophthalates of British Patent 766,290 and Canadian 562,672 and those obtainable by condensing terephthalic acid or dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyclohexane 1,4 dimethanol (hexahydro-p-xylene alcohol). Other high molecular weight, oriented polyesters such as polycarbonates are also useful. A

Swindells U.S. Patent 2,698,235 discloses, as aparticular useful subbing layer for the films disclosed above,- a very thin layer of a tri-component copolymer of vinylidene chloride, an acrylic ester, and itaconic acid. coated under controlled conditions. Other subbing compositions suitable for use on polyester films are those disclosed tive humidity. The matting coat is flexible while having an excellent drafting surface, is resistant to abrasion and does not become brittle or flake ofl during tough han1-- dling. An acrylic polymer such as used as a binding material in the examples of this application is particularly advantageous because, in addition to its great hardness, it has little or no tendency to discolor or deteriorate upon exposure to ultraviolet radiation or after prolonged aging. Also, a drafting layer comprising such a binding material is extremely resistant to flaking. A particularly unique advantage of this invention is the absence of migratory chemicals in the drafting layer which can cause dimensional change in the drafting layer with age or which would be capable of causing the hardening or cross-linking of gelatin in subsequently applied subbing layersor light-sensitive layers. It is because of this absence of cross-linking agents that it is possible to overcoat the drafting film with a wash-off gelatino-silver halide emulsion which can be preferentially hardened under the action of light and subsequent development. Still further advantages will be apparent from the above description of the invention.

What is claimed is:

1. A dimensionally stable drafting film comprising (1) a biaxially-oriented polyester film of at least one dicarboxylic acid and at least one dihydric alcohol having on at least one surface, in order (2) an essentially hydrophobic vinylidene chloride copolymer containing atleast 35 by weight of vinylidene chloride and (3) a hydrophobic film layer of methyl methacrylate polymer havinga Tukon film hardness above 10 KHN, said film containing up to 1 part by weight of matting agents per 1 part of said acrylate polymerand a silica hydrosol having about 3 to 25% of silicon dioxide based upon the weight of said acrylate polymer.

2. A drafting film as defined in claim 1 where said matting agents are present in an amount of about 0.3 to 0.8 part by weight per one part of said acrylate polymer.

3. A dimensionally stable drafting film comprising (1) a biaxially-oriented polyester film of at least one dicarboxylic acid and at least one dihydric alcohol havingon at least one surface in order (2) an essentially hydrophobic vinylidene chloride copolymer containing at least 35% by weight of vinylidene chloride and (3) a hydrophobic film layer of methyl methacrylate polymer having a Tukon film hardness above 10 KHN, said film containing a silica hydrosol having about 3 to 25% of silicon dioxide based upon the weight of said acrylate polymer and up to 1 part by weight of matting agents per 1 part 'of said acrylate polymer, the matting agentshavingv a particle size of about 0.1 to 10 microns.

4. A drafting film as defined in claim 3-Where' said particle size is about 1 to 10 microns.

5. A drafting film as defined in claim 3 where said matting agent is silicon dioxide.

6. A drafting film as defined in claim 3 where said matting agent is rice starch. y

7. A drafting film as defined in claim-.3 where said hydrophobic film layer has up to 0.05 part per 1 partof said acrylate polymer of a 1:1 copolymer of methylvinylether and maleic anhydride.

8. A dimensionally stable drafting film comprising (1) a biaxially-oriented polyester film of a dicarboxylic acid and a dihydric alcohol having on at least one surface, in order (2) an essentially hydrophobic vinylidene chloride copolymer containing at least 35% by weight of vinylidene chloride (3) a hydrophobic film layer of methyl methacrylate polymer having a Tukon film hardness above KHN, said film containing up to 1 part by weight of matting agents per 1 part of said acrylate polymer and (4) a gelatino-silver halide photographic emulsion, said emulsion being bound to said acrylate polymer layer by the polymerization product of a member selected from the group consisting of a single vinyl monomer and mixtures of vinyl monomers polymerized in an aqueous gelatin solution.

9. A drafting film as described in claim 8 where said vinyl monomer is selected from the group consisting of methyl acrylate, ethyl acrylate and vinylidene chloride.

10. A dimensionally stable drafting film comprising (1) a biaxially-oriented polyester film of a dicarboxylic acid and a dihydric alcohol having on at least one surface, in order (2) an essentially hydrophobic vinylidene chloride copolymer containing at least 35% by weight of vinylidene chloride (3) a hydrophobic film layer of methyl methacrylate polymer having a Tukon film hardness above 10 KHN, said film containing up to 1 part by weight of matting agents per 1 part of said acrylate polymer and (4) a wash-off gelatino-silver halide photographic emulsion containing a tanning developing agent, said emulsion being bound to said acrylate polymer layer by the polymerization product of a monomer selected from the group consisting of methyl acrylate, ethyl acrylate, vinylidene chloride and mixtures of said monomers polymerized in an aqueous solution of gelatin, said polymerization product being free from gelatin hardeners.

11. A process for preparing a drafting film having a biaxially-oriented polymeric polyester base covered with a thin layer of a vinylidene chloride copolymer which comprises (1) coating said layer with an aqueous dispersion containing a methyl methacrylate polymer having a Tukon hardness of greater than 10 KHN, a matting agent and a heat-removable coalescent material and (2) heating the film above 60 C. to remove said coalescent.

12. A process for preparing a drafting film having a biaxially-oriented polymeric polyester base covered with a thin layer of a vinylidene chloride copolymer which comprises (1) coating said layer with an aqueous dispersion containing -a methyl methacrylate polymer having a Tukon hardness of greater than 10 KHN, a matting agent and a heat-removable coalescent material (2) heating the film above 60 C. to remove said coalescent (3) applying a subbing layer, upon said acrylate polymer, comprising of a surfactant and the polymerization product of a member selected from the group consisting of vinyl monomers and mixtures of said monomers polymerized in an aqueous gelatin solution and (4) covering said subbing layer with a photographic gelatino-silver halide emulsion.

13. A process for preparing a drafting film having a biaxially-oriented polymeric polyester base covered with a thin layer of a vinylidene chloride copolymer which comprises (1) coating said layer with an aqueous dispersion containing a methyl methacrylate polymer having a Tukon hardness of greater than 10 KHN, a matting agent and a heat-removable coalescent material (2) heating the film above 60 C. to remove said coalescent, and (3) applying a layer having a gelatino-silver halide photographic emulsion, and the polymerization product of a member selected from the group consisting of vinyl monomers and mixtures of said monomers polymerized in an aqueous gelatin solution.

14. A process as defined in claim 13 wherein said heatremovable coalescent material is ethylene glycol, propylene glycol or diethylene glycol.

15. A dimensionally stable drafting film comprising (1) a biaxially-oriented polyester film of a dicarboxylic acid and a dihydric alcohol having on at least one surface, in order (2) an essentially hydrophobic vinylidene chloride copolymer containing at least 35% by Weight of vinylidene chloride (3) a hydrophobic film layer of methyl methacrylate polymer having a Tukon film hardness above 10 KHN, said film containing up to 1 part by weight of matting agents per 1 part of said acrylate polymer and (4) a wash-off silver-halide photographic emulsion having as its binder the polymerization product of a member selected from the group consisting of a single vinyl monomer and mixtures of vinyl monomers polymerized in an aqueous gelatin solution, said emulsion additionally containing a tanning developing agent.

16. A product as defined in claim 15 where said vinyl monomer is selected from the group consisting of methyl acrylate, ethyl acrylate, vinylidene chloride and mixtures of said monomers.

17. A dimensionally stable drafting film comprising (1) a biaxially-oriented polyester film of a dicarboxylic acid and a dihydric alcohol having on at least one surface, in order (2) an essentially hydrophobic vinylidene chloride copolymer containing at east 35% by weight of vinylidene chloride (3) a hydrophobic film layer of methyl methacrylate polymer having a Tukon film hardness above 10 KHN, said film containing up to 1 part by weight of matting agents per 1 part of said acrylate polymer (4) a substratum comprised of a reaction product prepared by polymerizing a monomer selected from the group consisting of methyl acrylate, ethyl acrylate, vinylidene chloride and mixtures thereof and an aqueous solution of gelatin, and (5) a wash-off gelatino-silver halide photographic emulsion containing a tanning developing agent.

18. A product as defined in claim 17 wherein said substratum (4) contains an amphoteric surfactant.

References Cited UNETED STATES PATENTS 2,360,216 10/1944 Fillius 9 2,536,657 11/1951 Reese 117--138.8 2,964,423 12/ 1960' Van Stappen 117-76 3,115,420 12/1963 Centa et al. 117-68 3,227,576 1/ 1966 Van Stappen 11776 NORMAN G. TORCHIN, Primary Examiner.

R. H. SMITH, Assistant Examiner. 

1. A DIMENSIONALLY STBLE DRAFTING FILM COMPRISING (1) A BIAXIALLY-ORIENTED POLYESTER FILM OF AT LEAST ONE DICARBOXYLIC ACID AND AT LEAST ONE DIHYDRIC ALCOHOL HAVING ON AT LEAST ONE SURFACE, IN ORDER (2) AN ESSENTIALLY HYDROPHOBIC VINYLIDENE CHLORIDE COPOLYMER CONTAINING AT LEAST 35% BY WEIGHT OF VINYLIDENE CHLORIDE AND (3) A HYDROPHOBIC FILM LAYER OF METHYL METHACRYLATE POLYMER HAVING A TUKON FILM HARDNESS ABOVE 10 KHN, SAID FILM CONTAINING UP TO 1 PART BY WEIGHT OF MATTING AGENTS PER 1 PART OF SAID ACRYLATE POLYMER AND A SILICA HYDROSOL HAVING ABOUT 3 TO 25% OF SILICON DIOXIDE BASED UPON THE WEIGHT OF SAID ACRYLATE POLYMER. 